U.S. patent application number 13/699232 was filed with the patent office on 2013-07-18 for method for culturing adipocytes.
This patent application is currently assigned to ASSISTANCE PUBLIQUE-HOPITAUX DE PARIS. The applicant listed for this patent is Karine Clement, Mayoura Keophiphath, Daniele Lacasa, Vanessa Pellegrinelli. Invention is credited to Karine Clement, Mayoura Keophiphath, Daniele Lacasa, Vanessa Pellegrinelli.
Application Number | 20130183706 13/699232 |
Document ID | / |
Family ID | 42938483 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130183706 |
Kind Code |
A1 |
Lacasa; Daniele ; et
al. |
July 18, 2013 |
Method for Culturing Adipocytes
Abstract
The present invention relates to a method for culturing
adipocytes, in which a homogeneous population of mature adipocytes
isolated from adipose tissue is cultured on a three-dimensional
culture substrate.
Inventors: |
Lacasa; Daniele; (Poissy,
FR) ; Pellegrinelli; Vanessa; (Juvisy sur Orge,
FR) ; Keophiphath; Mayoura; (Paris, FR) ;
Clement; Karine; (Paris, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lacasa; Daniele
Pellegrinelli; Vanessa
Keophiphath; Mayoura
Clement; Karine |
Poissy
Juvisy sur Orge
Paris
Paris |
|
FR
FR
FR
FR |
|
|
Assignee: |
ASSISTANCE PUBLIQUE-HOPITAUX DE
PARIS
Paris
FR
UNIVERSITE PIERRE ET MARIE CURIE (PARIS 6)
Paris
FR
|
Family ID: |
42938483 |
Appl. No.: |
13/699232 |
Filed: |
May 23, 2011 |
PCT Filed: |
May 23, 2011 |
PCT NO: |
PCT/IB11/52241 |
371 Date: |
February 6, 2013 |
Current U.S.
Class: |
435/29 ;
435/366 |
Current CPC
Class: |
C12N 2501/39 20130101;
C12N 2533/50 20130101; C12N 5/0653 20130101; G01N 33/5044
20130101 |
Class at
Publication: |
435/29 ;
435/366 |
International
Class: |
C12N 5/071 20060101
C12N005/071 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2010 |
FR |
10 02180 |
May 25, 2010 |
FR |
1002180 |
Claims
1. A method of culturing adipocytes, comprising culturing a
homogeneous population of mature adipocytes isolated from adipose
tissue on a three-dimensional culture substrate.
2. The method for culturing adipocytes as claimed in claim 1,
wherein the three-dimensional culture substrate is a hydrogel.
3. The method for culturing adipocytes as claimed in claim 1 or 2,
wherein the three-dimensional culture substrate is a hydrogel
formed from the noncovalent association of peptides comprising from
10 to 30 residues.
4. The method for culturing adipocytes as claimed in claim 3,
wherein the peptides comprise the sequence
R-A-D-A-R-A-D-A-R-A-D-A-R-A-D-A (SEQ ID NO: 11).
5. The method for culturing adipocytes as claimed in one of claim
1, wherein the adipose tissue was taken from one or more human
individuals.
6. An adipocyte culture, comprising a monoculture of mature
adipocytes isolated from adipose tissue, in contact with a
three-dimensional culture substrate.
7. The adipocyte culture as claimed in claim 6, wherein the adipose
tissue was taken from one or more human individuals.
8. A method of screening compounds which modulate adipocyte
metabolism comprising contacting the compound with an adipocyte
culture as defined in claim 6 and measuring adipocyte metabolism,
wherein a change in adipocyte metabolism indicates a compound which
modulates adipocyte metabolism.
9. The method as claimed in claim 8, further comprising screening
compounds which activate lipolysis.
10. The method as claimed in claim 8, further comprising screening
compounds which activate the PPAR.gamma.2 transcription factor.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method for culturing adipocytes,
to an adipocyte culture, and to the use thereof for screening
compounds which modulate adipocyte metabolism.
TECHNICAL BACKGROUND
[0002] The prevalence of obesity, linked to a hypertrophy of white
adipose tissue, is constantly increasing in the general population.
Thus, the proportion of individuals who are overweight or obese has
progressed from 36.7% to 41.6% between 1997 and 2003 in France; in
addition, the prevalence of obesity (defined by a body mass index
(BMI) of greater than 30 kg/m.sup.2) in France was 14.5% in 2009.
Moreover, obesity is a risk factor for many pathological disorders,
including in particular cardiovascular events, making its
therapeutic treatment all the more urgent.
[0003] While the main axes for combating this epidemic remain an
improved diet and an increase in physical exercise in obese
individuals, other approaches, in particular surgical and
drug-based, have also been explored.
[0004] The current drug-based approaches aim mainly to reduce
energy intakes, for example by limiting the intestinal absorption
of lipids (orlistat), or by reducing the appetite, either by
promoting the sensation of satiety (sibutramine) or by reducing the
pleasure associated with food intake (rimonabant).
[0005] However, the limited effectiveness of these methods or their
side effects--it has thus been reported that rimonabant can cause
severe depressive disorders--have in particular led to the
withdrawal of sibutramine and rimonabant from the market, leaving
therapeutic options very limited and making it necessary to explore
other approaches, making it possible, for example, to modulate the
metabolism of adipocyte cells in order to limit lipid storage or,
conversely, to promote the use thereof.
[0006] The latter approach is, however, made difficult to tackle by
the lack of in vitro or animal models for studying adipocyte
metabolism that are truly representative of the in vivo situation
in humans.
[0007] Indeed, as regards in vitro models, mature adipocyte cells,
in particular characterized by the presence of a single lipid
vacuole, which form the white adipose tissue, are particularly
fragile and, in fact, these cells generally lose their metabolic
and secretory properties in culture in less than 48 h.
[0008] Several culture systems have thus been proposed in order to
overcome these difficulties. However, these cultures comprise
supplementary cell types in addition to the adipocytes, such as
preadipocytes or endothelial cells (Sonda et al. (2008)
Endocrinology 149:4794-4798) or are prepared generally using
adipocytes differentiated in vitro from stem cells (Choi et al.
(2010) Tissue Engineering: Part C, Kang et al. (2007) Biomaterials
28:450-458) or from preadipocytes (Daya et al. (2007)
Differentiation 75:360-370, WO 2007/113591, Stacey et al. (2009)
Tissue Engineering: Part A 15:3389-3399), the phenotype of which is
relatively remote from that of mature adipocytes isolated from
adipose tissue (see FIGS. 1 to 3).
[0009] Thus, these systems do not appear to be specifically and
directly representative of the metabolism of mature adipocytes
isolated from adipose tissue.
[0010] An object of the present invention is therefore to provide
such a culture system, which is close to the physiological
situation, in particular close to human physiology.
SUMMARY OF THE INVENTION
[0011] The present invention results from the unexpected
demonstration, by the inventors, that mature adipocytes isolated
from adipose tissue can be cultured, in the absence of other cell
types, using a three-dimensional culture substrate and that the
adipocytes thus cultured retain, for at least 48 h, a phenotype
similar to that of freshly isolated mature adipocytes.
[0012] The present invention thus relates to a method for culturing
adipocytes, in which a homogeneous population of mature adipocytes
isolated from adipose tissue is cultured on a three-dimensional
culture substrate.
[0013] The present invention also relates to an adipocyte culture,
comprising a monoculture of mature adipocytes isolated from adipose
tissue, in contact with a three-dimensional culture substrate.
[0014] The invention also relates to the use of an adipocyte
culture according to the invention, for screening compounds which
modulate adipocyte metabolism.
[0015] The invention also relates to a method for screening
compounds which modulate adipocyte metabolism, in which: [0016] a
compound to be screened is brought into contact with an adipocyte
culture according to the invention; [0017] it is determined whether
at least one representative parameter of adipocyte metabolism, of
the adipocyte culture, is modified compared with an adipocyte
culture according to the invention which has not been brought into
contact with the compound to be screened; [0018] the compound is
selected if it modifies at least one representative parameter of
adipocyte metabolism.
DETAILED DESCRIPTION OF THE INVENTION
[0019] As it is intended here, the expression "mature adipocytes"
represents differentiated adipocytes. Mature adipocytes can be
easily identified by those skilled in the art. In particular, a
mature adipocyte according to the invention usually has a single
lipid vacuole, lipolytic activity, in particular inducible by
.beta.-adrenergic agents, such as epinephrine and norepinephrine,
and also a sensitivity to insulin, in particular defined by
insulin-inducible transport, from the extracellular medium to the
intracellular medium, of glucose and of fatty acids, which
transport is in particular linked to the insulin-dependent
translocation, within the plasma membrane of mature adipocytes, of
the GLUT-4 and CD36 transporters, respectively. The mature
adipocytes according to the invention differ in particular from
preadipocytes, notably in that the expression of the
preadipocyte-specific marker DelK1/Pref1, well known to those
skilled in the art, which can be measured by real-time PCR, is
essentially absent in the mature adipocytes according to the
invention.
[0020] The mature adipocytes according to the invention are
isolated from adipose tissue. Thus, the mature adipocytes according
to the invention are in particular such that they do not come from
the in vitro differentiation of adipocyte precursors, such as
preadipocytes or totipotent, multipotent or pluripotent stem
cells.
[0021] As regards the adipose tissue according to the invention, it
can come from any animal species. However, it is preferable for the
adipose tissue according to the invention to have been taken from
one or more human individuals.
[0022] The mature adipocytes can be isolated from adipose tissue by
numerous methods well known to those skilled in the art, taking in
particular advantage of the low density of mature adipocytes. In
particular, the adipose tissue can be treated with collagenase, and
then, after digestion, be filtered through woven cotton gauze; the
filtrate is left to settle out in an aqueous medium and a
homogeneous population of mature adipocytes according to the
invention can be recovered by harvesting the floating cells.
[0023] As it is intended here, "a homogeneous population of mature
adipocytes" is in particular such that it is essentially free of
other cell types, in particular of endothelial cells or of
preadipocytes. In particular, a homogeneous population of mature
adipocytes according to the invention comprises less than 10%, more
particularly less than 5%, of cells other than mature adipocytes,
in particular of preadipocytes. The amount of preadipocytes in a
homogeneous population of mature adipocytes can be determined by
quantifying the number of cells expressing a preadipocyte-specific
marker, such as DelK1/Pref1, for example.
[0024] As it is intended here, a "monoculture of mature adipocytes"
is a culture of a homogeneous population of mature adipocytes.
[0025] A homogeneous population of mature adipocytes is said to be
"cultured" or "in culture" when it is incubated, i.e. conserved in
vitro, under conditions which allow the survival of the cells
making up the population. Such conditions and also the appropriate
culture media are well known to those skilled in the art. These
culture media are such that they contain all the elements, in
particular nutritive elements, capable of ensuring the survival of
the cells making up the population for at least 12 h, preferably at
least 24 h, more preferably at least 48 h. By way of example, the
population can be incubated in a DMEM/F12, 1%
penicillin-streptomycin, 50 nM insulin medium, with agitation, at
37.degree. C. and in a 5% CO.sub.2 atmosphere, the medium being
regularly renewed. Advantageously, the culture media for the mature
adipocyte according to the invention can comprise compounds
intended to modulate the metabolic activity of the mature
adipocytes, such as forskolin and dexamethasone, for example.
Moreover, the culturing of the population of mature adipocytes is
preferably carried out for at least 3 h, 6 h, 12 h, 24 h or 48
h.
[0026] According to the invention, the mature adipocytes are
"cultured on a three-dimensional culture substrate" when the
adipocytes are in contact with the substrate, i.e. when they lie on
the substrate or when they adhere to the substrate.
[0027] In one particular embodiment, the method for culturing
adipocytes according to the invention comprises the following
steps: [0028] bringing a homogeneous population of adipocytes into
contact with a three-dimensional culture substrate; [0029]
incubating the mature adipocytes in contact with the culture
substrate, in particular under conditions which allow the survival
of the cells, in particular for at least 48 h.
[0030] A "three-dimensional culture substrate" according to the
invention consists of a material, in particular a biocompatible
material, suitable for obtaining a three-dimensional culture of
cells; in other words, the three-dimensional culture substrate is
suitable, in particular, for obtaining several superimposed cell
layers. Thus, a culture substrate which only allows the culturing
of a two-dimensional cell layer, namely a monolayer of cells, is
not a three-dimensional culture substrate according to the
invention.
[0031] Preferably, the three-dimensional culture substrate
according to the invention is a hydrogel. More preferably, the
three-dimensional culture substrate according to the invention is a
hydrogel formed from the noncovalent association of peptides
comprising from 10 to 30 residues, such as peptides comprising a
repeat of the sequence R-A-D-A, and in particular a sequence
R-A-D-A-R-A-D-A-R-A-D-A-R-A-D-A (SEQ ID NO: 11). The peptides
forming the hydrogen can be modified, for example by the addition
of acetyl groups to the N-terminal end of the peptides and by the
addition of an --NH.sub.2 group at the C-terminal end of the
peptides. Thus, the peptides can be represented by the sequence:
Ac-R-A-D-A-R-A-D-A-R-A-D-A-R-A-D-A-CONH.sub.2. Particularly
preferably, the three-dimensional culture substrate according to
the invention is the PuraMatrix.TM. hydrogel (3DM, Inc.).
[0032] The compounds capable of being screened according to the
invention may be of any type. In particular, they may be compounds
derived from chemical libraries. Moreover, the adipocyte culture
according to the invention can be used to screen for compounds
which activate lipolysis, or compounds which activate the
PPAR.gamma.2 transcription factor; or compounds which modulate
insulin sensitivity.
[0033] As it is intended here, lipolysis (or lipolytic activity),
insulin sensitivity, or PPAR.gamma.2 transcription factor activity
are representative parameters of adipocyte metabolism.
[0034] The determination of lipolysis can be carried out by
numerous methods well known to those skilled in the art. In
particular, lipolytic activity can be determined by measuring the
amount of glycerol and of free fatty acids that is released by an
adipocyte culture according to the invention, in particular by
spectrophotometry, as is described in Lacasa et al. (1991)
Endocrinology 128:747-753. The insulin sensitivity of adipocytes
can be evaluated according to the measurement of glucose transport
in the adipocyte, as is described in Wood et al. (2007) Biochem.
Biophys. Res. Commun. 361:468-473. The PPAR.gamma.2 transcription
factor activity can be measured by determining the amount of mRNA
encoding it in a cell, for example by RT-PCR, or by direct
measurement of the binding activity to its specific DNA sites, as
is in particular described in Keophiphath et al. (2009) J. Nutr.
139: 2055-2060.
DESCRIPTION OF THE FIGURES
[0035] FIGS. 1 to 3 represent, respectively, the relative
expression level (y-axis, arbitrary units), measured by real-time
PCR, of three markers specific for mature adipocytes, namely
PPAR.gamma.2, FABP4 (a fatty acid transporter, the gene of which is
a PPAR.gamma.2 target) and an adipokine, adiponectin, in, on the
one hand, mature adipocytes freshly isolated from adipose tissue
(black bars) and in, on the other hand, adipocytes obtained by in
vitro differentiation of preadipocytes, as is described in Lacasa
et al. Endocrinology 148:868-877 (white bars).
[0036] FIG. 4 represents an immunoelectrophoresis gel of cell
lysates prepared from mature adipocytes maintained in culture on
the three-dimensional substrate for 48 hours (3D) and from freshly
isolated mature adipocytes (D0), and then labeled using an antibody
directed against the aP2/FABP4 adipocyte marker and an antibody
directed against a positive control (actin).
[0037] FIGS. 5 and 6 represent, respectively, the levels of basal
and forskolin (FK)-stimulated lipolytic activity (y-axis, in
arbitrary units) of mature adipocytes cultured (i) in the
three-dimensional culture substrate (3D) in the absence (white
bars) and in the presence (black bars) of dexamethasone (Dex), and
(ii) in monolayers (2D) (gray bars), as a function of the culture
time (x-axis, in days). The experiment presented is representative
of a set of three replicated experiments.
[0038] FIGS. 7 and 8 represent, respectively, the amounts of leptin
and of adiponectin secreted (y-axis, in pg/ml/24 h) by mature
adipocytes cultured in the three-dimensional culture substrate (3D)
in the absence (white bars) and in the presence (black bars) of
dexamethasone (Dex). The experiment presented is representative of
a set of three replicated experiments.
[0039] FIG. 9 represents the relative gene expression of adipocyte
markers (y-axis, arbitrary units), measured by real-time PCR, using
extracts of freshly isolated mature adipocytes (black bars) and of
mature adipocytes maintained for 48 h in culture in the
three-dimensional culture substrate (white bars).
[0040] FIG. 10 represents an immunoelectrophoresis gel of cell
lysates prepared from mature adipocytes maintained in culture on
the three-dimensional substrate for 48 hours (3D) and from freshly
isolated mature adipocytes (2D) incubated in the presence of
insulin (10 nM) with the times indicated, and then labeled using an
antibody directed against the phosphorylated form of Akt and an
antibody directed against a positive control (actin).
EXAMPLES
A. Materials and Methods
1. Materials
[0041] The BD.TM. PuraMatrix.TM. peptide hydrogel is obtained from
BD Biosciences (Two Oak Park, Bedford, Mass., USA).
[0042] The anti-caveolin-1 (N-20, SC-894) and anti-CD36 (1.BB.3414,
CS-70642) primary antibodies used come from Santa Cruz
Biotechnology (Santa Cruz, Calif., USA). The corresponding
antibodies coupled to Cy3 are obtained from GE Healthcare (Little
Chalfont, UK).
2. Preparation of the Isolated Mature Adipocytes
[0043] The mature adipocytes are isolated by collagenase treatment
of human adipose tissue. The subcutaneous human adipose tissue of
young women (<45 years) who are not obese (BMI<30) is cut up
in digestion medium (DMEM, 2% essentially fatty acid free albumin
(A6003, Sigma, St Louis, Mich., USA), 1 mg/ml collagenase A (Roche
Diagnostics, Mannheim, Germany)) in the proportion of 1 g of tissue
per 2 ml of digestion medium in polypropylene tubes. The tubes are
placed at 37.degree. C. for minutes with agitation (200
cycles/minute). After digestion, the medium is filtered through
woven cotton gauze. The mature adipocytes are left to decant by
floating for 5 minutes and are then washed 3 times with 5 volumes
of 10% sucrose. At the end of the final wash, the sucrose is
removed and the mature adipocytes are ready to be incorporated into
the PuraMatrix.TM. hydrogel.
3. Preparation of the Hydrogel Containing the Mature Adipocytes
[0044] As recommended by the manufacturer, the hydrogel is
sonicated for 30 minutes in order to reduce its viscosity. The gel
is then diluted V/V with 20% sucrose and then centrifuged for 5
minutes at 1000 g in order to remove the air bubbles. The washed
mature adipocytes are rapidly incorporated into this mixture with
homogenization via gentle suction with a pipette. The
adipocytes/gel mixture is then distributed, in the proportion of
100 .mu.l per well, into 96-well culture plates. Very rapidly, the
incubation medium (150 .mu.l) (DMEM/F12, 1%
penicillin-streptomycin, 50 nM insulin) (DMI) is added to the wells
and the plates are placed in an incubator at 37.degree. C. under a
5% CO.sub.2 atmosphere. After 30 minutes, the DMI medium is
renewed. The change in medium is repeated twice. The following day,
the DMI medium is changed, and this operation is repeated every
day. In some experiments, the DMI contains 100 nM dexamethasone
(Sigma Aldrich, St Louis, Mo., USA) or 100 nM of rosiglitazone
(Merck, Nottingham, UK).
4. Measurement of Lipolytic Activity
[0045] The wells containing the hydrogel/adipocytes combination are
washed a first time with 150 .mu.l of Krebs-Ringer medium (115 mM
NaCl, 4.7 mM KCl, 1.2 mM CaCl.sub.2, 1.2 mM KH.sub.2PO.sub.4, 1.2
mM MgSO.sub.4, 20 mM NaHCO.sub.2), 5 mM glucose, 3% essentially
fatty acid free albumin (KRB/ALB), in order to equilibrate the
hydrogel. 100 .mu.l of KRB/ALB containing either 0.1% DMSO or 10
.mu.M forskolin (Sigma) are distributed into the wells. The plates
are then placed in the incubator for 4 hours. The medium is sampled
and placed at 70.degree. C. for 10 minutes in order to inactivate
the adipocyte enzymes that can interfere with the glycerol assay.
The glycerol released is assayed by spectrophotometry (Glycerol
assay kit, R-Biopharm) as described in Lacasa et al. (1991)
Endocrinology 128:747-753.
5. Measurement of Adipokine Secretion
[0046] The DMI medium is sampled 24 hours after the final change of
medium. The assay of the adipokines (leptin, adiponectin) is
carried out directly on this medium (100 .mu.l) using the ELISA
technique (Duoset, R&D Systems, Minneapolis, Minn., USA) as
described by the manufacturer.
6. Measurement of Gene Expression
[0047] The DMI medium is rapidly removed from the wells and the
gel/adipocytes combination is homogenized with the lysis buffer in
the proportion of 1 ml of lysis buffer/1 ml of gel/adipocytes
combination. The RNAs are then extracted with, beforehand, a
delipidizing treatment with chloroform using the RNeasy extraction
kit (Qiagen, Courtaboeuf, France) as described in Lacasa et al.
(2007) Endocrinology 148:868-877. The total RNAs (1 .mu.g) are then
transcribed into cDNAs as described in Lacasa et al. (2007)
Endocrinology 148:868-877. The list of primers used is indicated in
table 1. The real-time PCR assays are carried out with 25 ng of
cDNA and the sense and antisense primers using the Sybergreen
universal PCR mix (Applied Biosystems, Minneapolis, Minn., USA) and
measured in a detection apparatus (Applied Biosystems). All the
values are standardized relative to the expression of the RPLPO
ribosomal protein.
TABLE-US-00001 TABLE 1 Primers used Gene Sense Antisense
Adiponectin TGTGATCTTGGCTCACTGTC CAGCTACTTGGGAGGCTGA (SEQ ID NO: 1)
(SEQ ID NO: 2) aP2/FABP4 CCTTTAAAAATACTGAGATTTCCTTCA
GGACACCCCCATCTAAGGTT (SEQ ID NO: 3) (SEQ ID NO: 4) Leptin
AGAAAGTCCAGGATGACACC GACTGCGTGTGTGAAATGTC (SEQ ID NO: 5) (SEQ ID
NO: 6) PPAR.gamma. CAGGAAAGACAACAGACAAATCA GGGGTGATGTGTTTGAACTTG
(SEQ ID NO: 7) (SEQ ID NO: 8) LPL ATGTGGCCCGGTTTATCA
CTGTATCCCAAGAGATGGACA (SEQ ID NO: 9) (SEQ ID NO: 10)
7. Immunofluorescence Techniques
[0048] After removal of the DMI medium and washing with PBS, the
gel/adipocytes combination is deposited in wells of 96-well plates
and fixed with 4% paraformaldehyde (PAF) for 1 hour. After
inactivation of the PAF by treatment with a PBS/0.1M glycine
buffer, the cells are permeabilized for 5 minutes at ambient
temperature with 0.1% Triton X-100 in PBS/3% albumin. The
nonspecific sites are blocked with the PBS/3% albumin buffer for 4
hours at ambient temperature, and then the primary antibodies are
added and the incubation is continued for 14 hours at 4.degree. C.
After 6 washes (1 hour), the gel/adipocytes combination is
incubated with the secondary antibodies for 4 hours at ambient
temperature in the dark. The gel/adipocytes combination is then
washed (1 hour) and fragments of this gel are placed in mounting
medium (Fluomount, Birmingham, Ala., USA) between slides and cover
slips. The slides are examined by fluorescence after 24 hours.
8. Immunoelectrophoresis Techniques
[0049] After removal of the DMI medium and washing with PBS, the
gel/adipocytes combination is rapidly lysed with one volume of
lysis buffer (PBS, 2% IGEPAL, 0.2% SDS, 1% sodium deoxycholate)
containing a mixture of protease inhibitors and phosphatase
inhibitors (Complete mini and Phosphostop, Roche Diagnostics). The
homogenate is then kept at 4.degree. C. for 15 minutes and then
centrifuged for 10 minutes at 5000 g. The cell lysate is then
collected and diluted in Laemmli buffer and subjected to
electrophoresis as described in Lacasa et al. (2007) Endocrinology
148:868-877. After transfer of the proteins onto a cellulose
membrane, staining with Ponceau red makes it possible to verify the
load and the quality of the transfer. The membranes are then
incubated with the primary antibodies at 4.degree. C. for 14 hours.
Then, after washes have been performed, the membranes are incubated
with the secondary antibodies (GE Healthcare, Little Chalfont, UK).
The signals are detected by chemiluminescence (Detection ECL, GE
Healthcare) and quantified by densitometry.
9. Measurement of Insulin Sensitivity
[0050] The wells containing the hydrogel/adipocytes deprived of
insulin the day before are incubated with the incubation medium
(150 .mu.l) (DMEM/F12 and 10 nM insulin). The plates are then
placed in the incubator for 15 to 30 minutes. The gel/adipocytes
combination is rapidly lysed with one volume of lysis buffer (PBS,
2% IGEPAL, 0.2% SDS, 1% sodium deoxycholate) containing a mixture
of protease inhibitors and phosphatase inhibitors (Complete mini
and Phosphostop, Roche Diagnostics). The homogenate is then kept at
4.degree. C. for 15 minutes and centrifuged for 10 minutes at 5000
g. The lysate is then collected and diluted in Laemmli buffer and
subjected to electrophoresis as described previously. The membranes
are then incubated with the primary antibodies directed,
respectively, against the phosphorylated form of Akt at the level
of Ser.sup.473 (ref. G7441, Promega) or against actin (positive
control) (MAB1501R, Millipore) at 4.degree. C. for 14 hours. Then,
after washes have been performed, the membranes are incubated with
the secondary antibodies (GE Healthcare, Little Chalfont, UK). The
signals are detected by chemiluminescence (Detection ECL, GE
Healthcare) and quantified by densitometry.
B. Results
1. Homogeneity of the Mature Adipocyte Population
[0051] The proportion of contaminating preadipocytes present in the
population of mature adipocytes isolated from adipose tissue used
for the culturing was determined by measuring, by real-time PCR,
the expression of the preadipocyte-specific marker DelK1/Pref1.
[0052] This measurement shows that the mature adipocyte population
used is essentially homogeneous, since it comprises less than 5% of
preadipocytes (approximately 4%).
2. Detection of Adipocyte Proteins
[0053] The mature adipocytes cultured in the three-dimensional
substrate formed by the hydrogel do exhibit a unilocular appearance
after immunofluorescence labeling of the membrane proteins CD36 and
caveolin-1, thereby demonstrating the possibility of detecting
adipocyte membrane proteins. Moreover, the adipocyte lysates can be
analyzed by immunoelectrophoresis, as shown by the detection of the
cytosolic adipocyte protein aP2/FABP4 and of actin (FIG. 4).
3. Lipolytic Activity
[0054] The lipolytic activity is measured under basal conditions
and under conditions stimulated with 10 .mu.M of forskolin on the
mature adipocytes maintained in the hydrogel for 7 days. This
activity is also compared with that of the same cells freshly
isolated. The results given in FIGS. 5 and 6 show that the basal
lipolytic activity (FIG. 5) and the forskolin-stimulated lipolytic
activity (FIG. 6) are of the same order as those of freshly
isolated adipocytes, and remain constant for 5-7 days. Moreover,
the presence of dexamethasone (synthetic glucocorticoid) in the
culture medium does not modify the basal and stimulated
activities.
4. Secretion of Adipokines: Adiponectin and Leptin
[0055] The secretion of adiponectin (FIG. 7) and of leptin (FIG. 8)
is measured for as long as 7 days of maintaining the mature
adipocytes in the hydrogel in the presence or absence of
dexamethasone (synthetic glucocorticoid). Moreover, as is shown in
FIG. 7, the secretion of leptin decreases during the culturing in
the absence of dexamethasone, whereas this secretion increases in
the presence of the glucocorticoid, thus demonstrating that the
response to these hormones remains functional in the adipocytes in
culture. The secretion of adiponectin, for its part, remains
constant for 7 days (FIG. 8).
5. Adipocyte Gene Expression
[0056] The expression of adipocyte genes is compared between
freshly isolated mature adipocytes and the same cells maintained
for 2 days in hydrogel. FIG. 9 shows that the expression of the
adipokines (leptin and adiponectin), of the major adipocyte
transcription factor PPAR.gamma.2 and of its target genes aP2/FABP4
and LPL remains constant.
6. Measurement of Insulin Sensitivity
[0057] Adipocytes constitute a preferred target of insulin, which
is a major anabolic hormone. In human adipocytes, insulin
stimulates glucose consumption, causing increased synthesis of
triglycerides, and, on the other hand, inhibits the degradation of
these lipids. The Akt enzyme transmits the metabolic effects of
insulin, which causes its activation by phosphorylation of serine
473 (Ser.sup.473 Akt). Thus, the level of Akt phosphorylation
constitutes an index of insulin sensitivity of the cells.
[0058] Insulin (10 nM) stimulates the Akt phosphorylation in an
identical manner in freshly isolated adipocytes (2D) and those
maintained for 48 h in the hydrogel (3D), thus indicating good
maintenance of the response to insulin of these cells (FIG.
10).
CONCLUSIONS
[0059] The mature adipocytes maintained in a three-dimensional
culture substrate of hydrogel with an incubation medium, which can
be supplemented with glucocorticoids and thiazolinidinediones,
exhibit a lipolytic activity and an adipokine (leptin and
adiponectin) secretion activity comparable to those of freshly
isolated adipocytes. Furthermore, the mature adipocytes maintained
in the hydrogel retain, for at least 7 days, the ability to respond
to glucocorticoids, which are hormones essential for adipocyte
metabolism and development (Macfarlane et al. (2008) J. Endocrinol.
197:189-204).
[0060] Thus, this system can be used to screen for pharmacological
compounds which have lipolytic activities or activities activating
the adipo-specific transcription factor PPAR.gamma.2, for
example.
[0061] Moreover, the inventors have shown that the mature
adipocytes maintained in a three-dimensional culture substrate of
hydrogel according to the invention retain for at least 2 days
their insulin sensitivity, compared with freshly isolated mature
adipocytes. This confirms that the adipocyte culture according to
the invention is a model representative of mature adipocytes in
vivo.
Sequence CWU 1
1
11120DNAArtificial SequencePCR Primer 1tgtgatcttg gctcactgtc
20219DNAArtificial SequencePCR Primer 2cagctacttg ggaggctga
19327DNAArtificial SequencePCR Primer 3cctttaaaaa tactgagatt
tccttca 27420DNAArtificial SequencePCR Primer 4ggacaccccc
atctaaggtt 20520DNAArtificial SequencePCR Primer 5agaaagtcca
ggatgacacc 20620DNAArtificial SequencePCR Primer 6gactgcgtgt
gtgaaatgtc 20723DNAArtificial SequencePCR Primer 7caggaaagac
aacagacaaa tca 23821DNAArtificial SequencePCR Primer 8ggggtgatgt
gtttgaactt g 21918DNAArtificial SequencePCR Primer 9atgtggcccg
gtttatca 181021DNAArtificial SequencePCR Primer 10ctgtatccca
agagatggac a 211116PRTArtificial SequencePeptide constituent of a
hydrogel 11Arg Ala Asp Ala Arg Ala Asp Ala Arg Ala Asp Ala Arg Ala
Asp Ala 1 5 10 15
* * * * *